As known in the prior art, in order to comply with mandatory pollutant emission limits, in new-generation vehicles, and in particular motor vehicles provided with a modern indirect injection petrol engine with three-way catalyst, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric value, in order to reduce exhaust gas emissions.
For that purpose, modern motor vehicles are generally provided with an airflow meter (debimeter) which is usually installed in the air intake system of the engine and provides an electric signal indicative of the flow rate of the fresh air supplied to the engine, on the basis of which the electronic control unit calculates the fuel flow rate to be injected into the engine cylinders before opening the intake valves, also as a function of the desired air-fuel ratio.
Alternatively, new-generation vehicles are known which are provided with an electronic control unit that, among other functions, implements an algorithm to estimate the intake air flow rate in the engine.
In particular, controlling the air-fuel ratio precisely at close to the stoichiometric value is particularly difficult in new-generation motor vehicles provided with a continuously variable intake timing system.
In this type of engine, measuring or precisely estimating the instantaneous mass of air flowing into the cylinders is particularly complicated, mainly owing to the natural supercharging effect that occurs in such engines due to the timing of the pressure waves in the intake manifold when the intake valve is opened.
In particular, when an airflow meter is used in an engine with a variable timing system, the air mass flowing into the cylinders cannot be measured precisely, due to the slow dynamics of the airflow meter, which is therefore unable to react to the extremely non-linear dynamics of the air passing through the intake conduit, characterized, even in normal driving conditions, by fast transients.
Research conducted by the applicant has also demonstrated that even when the known algorithms are used it is not possible to obtain a precise estimation of the mass of air entering variable timing engines. In fact, such algorithms do not consider the positive displacement pump effect of the engine at changes in speed, which have a marked influence on the intake air mass flow rate, especially in high pressure areas, for instance with pressure ratios at the throttle valve in the region of 0.9-0.95, or any mechanical timing errors, or any sudden changes in the intake timing, nor are they capable of correctly reproducing transitions between torque law and mechanical law in the status of the Drive-by-Wire control system.